Bearings

ABSTRACT

A method of manufacturing a bearing is described, the method comprising the steps of preparing a flat blank having a steel backing layer and a bearing alloy lining, the blank having an area corresponding to the projected surface area of the bearing, the flat blank also having required bearing features such as oil holes, grooves, and end-face chamfers and forming the flat blank directly into an associated bearing housing. The thickness of the flat blank should lie in the range from 0.25 to 0.75 mm. The blank may correspond in major dimension to a half bearing or to a full cylindrical bush.

The present invention relates to bearings and particularly to a methodof making bearings known as thin-wall bearings.

Thin-wall half bearings are currently made by a long, complex andexpensive series of mechanical forming and machining steps. The presentmethod begins with a strip or coil of material which generally comprisesa steel backing layer having thereon a bearing material lining. Thelining usually comprises a copper-based or aluminium-based alloy and hasbeen bonded to the steel by casting or sintering in the case ofcopper-based alloys or usually, by roll-pressure bonding in the case ofaluminium-based alloys. Depending upon the diameter of the bearing to bemade the strip material usually lies in thickness range from 1.5 mm to5.0 mm. Blanks slightly larger than the projected surface area of thedesired bearing are cut from strip and formed during several bendingoperations into a semi-cylinder after which the axial location nick isformed, the bearing end face chamfers are machined, the joint faces arebroached and final bore size is provided either by broaching or boring.Other operations such as the provision of oil holes, grooves etc. areusually also carried out on the part finished bearing when in asemi-cylindrical condition. The resulting finished half bearing may thenbe assembled directly into the main or big-end bearing housing in theengine.

It is generally acknowledged in the bearing art that, for a givenbearing lining material, the fatigue resistance of the lining increaseswith decreasing lining thickness. The final forming operation to producea semi-cylindrical part is known as coining, where the strip ends arestruck by a press punch to force the bent blank to conform tosemi-cylindrical die cup. Due to the coining operation, the material atthe joint face region undergoes a relatively considerable swelling dueto plastic compressive deformation. The swelling causes the residuallining thickness of the joint face region to be reduced after boringcompared to the lining thickness at the crown region of the bearing. Theeffect of such joint face swelling is to necessitate a thicker liningthan may be desirable.

Apart from the complexity and cost of the above production procedure,handling of the half bearings by machinery, such as robots, in automatedengine assembly lines is difficult. Automated assembly apparatus isbetter able to handle flat, rectangular pieces than semi-cylindricalpieces.

It is an object of the present invention to reduce the cost ofmanufacture of half bearings. It is a further objective to producepieces which are more easily handled by automated assembly apparatus. Itis a yet further objective to provide a method where joint face swellingis reduced.

According to the present invention there is provided a method ofmanufacturing a bearing, the method comprising the steps of preparing aflat blank having a steel backing layer and a bearing alloy lining, theblank having an area corresponding to the projected surface area of thebearing, the flat blank also having required bearing features such asoil holes and end-face chamfers and forming the flat blank directly intoan associated bearing housing.

It is desirable that the strip from which the flat blank is made isconsiderably thinner than has heretofore been customary. The blankthickness may lie in the range from 0.25 mm to 0.75 mm. The liningthickness may lie in the range from 0.1 mm to 0.25 mm and the steelbacking in the range from 0.15 mm to 0.525 mm.

The bearing blanks may be of a size such as to form a half bearing ormay be such as to constitute a full cylindrical bearing bush when formedinto the bearing housing.

An advantage of using a single blank to form a full cylindrical bush isthat it is easily handled and there is no danger of the free endsbecoming overlapped.

Advantageously the blanks are produced from a continuous strip ofmaterial comprising the steel and bearing alloy layers.

Preferably bearing blanks may be produced having their major dimensionparallel to the strip axis; this is commonly known as the down-stripdirection. By producing the blanks in this direction a wide strip may beslit accurately into strips having a width which corresponds to thefinal bearing axial length and may have any bearing end-face chamfersformed on the slit strip. Each blank may then be produced merely byblanking to an accurate length, perhaps with an intervening wasteportion and, after the other necessary features have been applied.

It is desirable to form all the bearing features on the blank when inthe flat condition since it is envisaged that after initial fitting ofthe blank to the bearing housing, the shaft will be installed and thehousing and it's associated cap secured together as a final operation.This, of course, does not necessarily preclude the present method beingused in place of the existing method of bearing production and removingthe formed bearing from its housing, or from a forming cup being used inplace of the housing, and providing formed half bearings to be used, forexample, in a bearing spares operation. Thus, any reference to housingin this specification also includes a forming cup or die. It should beremembered, however, that owing to the thinner material used in bearingsof the present invention, the degree of "freespread" on removing thebearing from its housing or forming cup will be much greater than for aconventional bearing. The "freespread" is the elastic spring back whichoccurs when a bearing is removed from its housing and adopts a dimensionacross the ends which is greater than the nominal diameter.

It is necessary to form the flat blank into its housing without theformation of any kinks or discontinuities which may affect the bearingsurface in relation to its hydrodynamic operation in, for example, areciprocating internal combustion engine or a piece of rotatingmachinery.

The total final wall thickness of the finished bearing may be producedeither by a deformation process such as rolling of the strip material orby machining of the lining or backing by milling, for example. Suchshaping may also include some compensation for anticlastic deformationwhich occurs during forming of the half bearing. The degree ofanticlastic deformation, however, is much less with the thinner materialof the present invention than in conventional bearings and as such, thisis an advantage.

In order that the present invention may be more fully understood anexample will now be described by way of illustration only with referenceto the accompanying drawings, showing a series of manufacturing stagesschematically depicted, of which:

FIG. 1 shows a strip being slit into bearing widths;

FIG. 2 shows a slit strip having joint face relief applied;

FIG. 3 shows the strip of FIG. 2 being chamfered;

FIG. 4 shows the strip of FIG. 3 in cross-section;

FIG. 5 shows the strip of FIG. 3 having an oil groove machined;

FIG. 6 shows the strip of FIG. 5 having an oil hole formed;

FIG. 7 shows the strip of FIG. 6 being machined to a desired wallthickness;

FIG. 8 shows the strip of FIG. 7 having a bearing blank separated andthe nick applied;

FIG. 9 shows the blank of FIG. 8 about to be formed into a bearinghousing;

FIG. 10 shows the co-operating cap half to the housing of FIG. 9 inplace;

FIGS. 11 to 13 show an alternative method to that illustrated in FIG. 9for forming the flat blank into its housing; and

FIGS. 14 to 17 which show schematic representations of a blank beingformed into a bearing housing to produce a full cylindrical bush.

Referring now to the drawings and where the same features are denoted bycommon reference numerals.

A coil of material 10 comprising a steel backing 12 of thickness 0.4 mmand having a lining 14 of A1 - Sn 20 - Cu 1 0.2 mm thick produced by acold, roll pressure bonding operation is slit into bearing widths 16 bysawing or shearing (FIG. 1). The width of the strips 16 corresponds tothe axial length of the final half bearing. FIG. 2 shows one of thestrips 16 having the lining 14 machined away in the regions 18 and whichwill correspond to the areas of joint face relief in the final bearing.The areas 18 are shown spanning the adjacent areas of two completeblanks 20, 22 and two part blanks 24, 26. The arrows 28 denote theapproximate position where the strip 16 will be cut into individualblanks. After the joint face relief is machined the strip 16 is thenchamfered 30 (FIGS. 3 and 4) to remove any burrs which may have beenproduced in earlier stages. The cross section at FIG. 4 shows the stripthickness and chamfers greatly exaggerated. An oil groove 32 (FIG. 5) isthen machined along the strip length followed by piercing of oil holes34 which are also deburred and chamferred. (FIG. 6). The lining 14 isnext machined to produce the final bearing wall thickness and anyallowance in cross sectional shape to cater for anticlastic deformation.(FIG. 7). The full blank 22 is removed in a single blanking operation bymeans of a fixed length die (not shown) which leaves a small piece ofscrap 36 and also produces the location and anti-rotation nick 38 (FIG.8). The following blank 20 has, at its leading edge 40 provision for thescrap piece 36 indicated by the dashed line 42. The finished, flat blank22 may then be formed into its housing 44 by means of the punches 46, 48which exert a constant bending moment on the blank 22 during forminginto the housing (FIG. 9). After the blank has been inserted into thehousing 44 the shaft 50 may be inserted and the co-operating cap-half 52togther with its associated bearing half 54 may be bolted to the housing44 (FIG. 10) to form the finished assembly; tightening of the cap half52 causing the two halves 22 and 54 to become fully seated.

Only very shallow oil grooves are possible when formed in the bearing.If greater oil flow is desired the groove may be formed in the housingwith additional oil access holes or a slot in the bearing.

Desirably the machining step to produce the finished lining thicknessshould be left as near as possible to the end of the production sequenceto minimise the risk of damage to the lining surface.

The blanks 22, 20 etc may alternatively be separated from the strip 16by sawing, the nick 38 being formed by pressing immediately beforeremoval of the scrap piece 36 and the blank 22 from the strip 16.

FIGS. 11 to 13 show an alternative sequence where the flat blank 22 ispushed into the housing 44 between a guide wheel 60, having an axis 62in the same plane as the joint faces 64, the periphery 66 of the housingbore and the top surface 68 of guide plate 70. The end having the nick38 is the last to enter the housing.

FIGS. 14 to 17 show schematically a sequence of steps to install a blank80 into a bearing housing 44 and cap 52 to form a full cylindrical bush82. The blank 90 is first laid across the housing 44 in a manner suchthat the butt ends 84, 86 lie in the position remote from the highlyloaded region of the bearing in operation. The shaft (shown as journal50) is then installed causing the ends 84,86 to become upstanding (FIGS.15). The ends 84, 86 are then squeezed in an inwardly direction to allowthe cap half 52 to be put in place. The act of tightening down the caphalf causes the bearing bush 82 to be formed.

We claim:
 1. A method of manufacturing a bearing, the method comprisingthe steps of preparing a flat blank having a steel backing layer and abearing alloy lining, the blank having an area corresponding to theprojected surface area of the bearing, forming in the flat blank anyrequired bearing features of the finished bearing, and forming the flatblank directly into an associated bearing housing.
 2. A method accordingto claim 1 wherein the thickness of said flat blank lies in the rangefrom 0.25 to 0.75 mm.
 3. A method according to claim 2 wherein thethickness of said bearing alloy lining lies in the range from 0.1 to0.25 mm.
 4. A method according to claim 2 wherein said steel backinglayer thickness lies in the range from 0.15 to 0.525 mm.
 5. A methodaccording to claim 1 wherein the thickness of said bearing alloy lininglies in the range from 0.1 to 0.25 mm.
 6. A method according to claim 1wherein said steel backing layer thickness lies in the range from 0.15to 0.525 mm.
 7. A method according to claim 1 wherein said blanks areproduced from a continuous strip of material.
 8. A method according toclaim 7 wherein said blanks are produced having their major dimensionparallel to the axis of the strip from which they are produced.
 9. Amethod according to claim 8 wherein a wide strip is slit into two ormore narrower strips having a width corresponding to the final bearingaxial length.
 10. A method according to claim 7 wherein a wide strip isslit into two or more narrower strips having a width corresponding tothe final bearing axial length.
 11. A method according to claim 9wherein chamfers are applied to the edges of the narrower strips.
 12. Amethod according to claim 10 wherein all of the featuring and sizingoperations are carried out on the strip prior to severing the blanktherefrom.
 13. A method according to claim 7 wherein all of thefeaturing and sizing operations are carried out on the strip prior tosevering the blank therefrom.
 14. A method according to claim 1 whereinthe blank major dimension corresponds to a half bearing.
 15. A methodaccording to claim 1 wherein the blank major dimension corresponds to afull cylindrical bush.
 16. A bearing blank when made by the method ofclaim 1 prior to fitting into a bearing housing.
 17. A bearing whenformed by the method of claim 1.